Java How to Program, Early Objects, 11th Edition

I.2 Streams

Input and output are usually performed with streams, which are sequences of bytes. In input operations, the bytes flow from a device (e.g., a keyboard, a disk drive, a network connection) to main memory. In output operations, bytes flow from main memory to a device (e.g., a display screen, a printer, a disk drive, a network connection).

When program execution begins, three streams are created. The standard input stream typically reads bytes from the keyboard, and the standard output stream typically outputs characters to a command window. A third stream, the standard error stream (System.err), typically outputs characters to a command window and is used to output error messages so they can be viewed immediately. Operating systems ...